Heretofore certain battery operated toys or novelty items, as variously termed, have been marketed that, when shaken, produce a noise or other sound in response. The nature of such responsive sound provides obvious amusement to the user. As example, a toy simulated frog, when so disturbed, produces a croaking sound, simulating, to a degree, a live frog's response.
In those kind of novelty items the motion sensor is included as part of an electrical circuit that is supplied with electrical current from batteries that are self-contained within the item. The batteries serve also to supply current to the audio generating circuits that produce the sound or alarm. When activated, as by shaking the novelty item and thereafter replacing that item in a stable position, the audio sound generation is initiated and, continues for a predetermined interval following cessation of the shaking action through appropriate action of time delay circuits contained within the item. This provides for the appropriate amusement for the user and also conserves the battery's energy.
As one appreciates, novelty items of this type are manufactured in high volume and, to be viable in the retail marketplace from the standpoint of price point, must be currently being marketed the device contained an inertia type motion sensor of very inexpensive construction that obviously satisfies the referenced cost consideration. The motion sensor, however, quickly developed the propensity to "stick"; that is, the inertia switch remained closed and, consequently, the toy emitted sound continuously, resulting in prematurely draining the electrical batteries that powered the toy. Although capable of detecting vibration and/or movement the amusement device was thus not reliable.
It is recognized that a motion sensor of more exotic construction may well serve to cure the reliability problem in the aforesaid device. However, known motion sensors of that type appear to be of a construction that is too expensive for use in novelty item application.
A motion sensor design is presented in U.S. Pat. No. 4,196,429, granted Apr. 1, 1980 to Davis. In that design a pair of cylinders of electrical insulator material are coaxially concentrically arranged to form an annular cylindrical cavity. The inner wall of the outer cylinder contains a series of electrical conductors arranged in two portions. Each portion is formed of spaced extending conductive fingers, including fingers of a zig-zag shape, and extend along the wall axial of the cylinder. The fingers of the two portions are interdigitally arranged and spaced to provide direct electrical isolation there between. An electrically conductive metal ball is loosely disposed within the annular cavity and bridges adjacent fingers, thereby closing an electrical circuit between the two portions of conductors. Suitably, any rolling movement of the ball along the axis of the structure or around the periphery results in the ball causing interruption in the electrical circuit by alternately bridging and un-bridging contacts between adjacent interdigitated conductive fingers. When an article carrying the sensor is moved or shaken the mechanical inertia of the confined metal ball causes the ball to effectively move or roll in the chamber relative to the chamber's walls, thereby creating numerous interruptions and initiations of electrical current flow. Accompanying electronic circuits detect the transition of the current, the current surge, and initiate action of an alarm.
Although the practicality and effectiveness of the motion detector design presented by Davis in novelty item application is not known, the principle of a metal ball to detect motion, evidenced in the Davis patent, appears well founded. The Davis structure is essentially three dimensional in nature; that is, it requires the formation of a pattern of electrical conductors on a curved surface, the cylinder wall. That curved arrangement may be accomplished in either of two ways: forming a circuit pattern on a cylindrical shaped circuit board, which appears difficult and, consequently, expensive, or, alternatively, forming the circuit arrangement on a flat, relatively flexible circuit board which, thereafter, may be formed or assembled into the cylindrical shape desired in the Davis structure. This latter assembly would also appear to add expense and increased difficulty to manufacture as detracts from novelty item application.
An object of the present invention is to provide a reliable low cost motion sensor construction of the simplest possible structure that uses the principal of the inertia of a metal ball to detect motion. It is a further object of the invention to provide a ball type motion sensor that does not require formation of electrical conductors onto curved surfaces. It is a still additional object of the invention to provide a low cost easily assembled motion detector for use in toy applications that has sufficient sensitivity to detect such slight vibrations as would be caused by stroking or petting the toy by hand. An ancillary object to the invention is to provide a motion sensor that may easily be integrated into, or be formed as part of, a printed circuit board containing the audio generators and other ancillary electronic circuits and which is suitable for robotic or machine assembly.